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Genetic counseling: Advanced Maternal Age - Chorionic Villus Sampling (CVS)-2
Advanced Maternal Age - Chorionic Villus Sampling (CVS) Contracting *How has your pregnancy been going? Have there been any complications? *What is your understanding of why you were referred for genetic counseling? *What specific questions/concerns would you like to address today? Maternal Age Associated Pregnancy Risks *Women over age of 35 considered at "high risk" for chromosomal abnormalities *Explain chromosomes and nondisjunction *Common trisomies associated with advanced maternal age **Trisomy 21 (Down Syndrome) ***Caused by presence of 3 copies of chromosome 21 ***Can result in characteristic facies, mild to moderate mental retardation, congenital heart disease and other health problems ***Varying range of severity ***Many children can go to school, adults may hold jobs and live semi-independantly **Trisomy 13 (Patau Syndrome) and Trisomy 18 (Edward Syndrome) ***Caused by presence of 3 copies of chromosome 13 or 18 ***More severe medical issues than those associated with Down Syndrome ***Usually fatal within first year of life **Klinefelter Syndrome (47,XXY) ***Caused by presence of an extra X chromosome ***Phenotypic males who may have small testes and androgen deficiency ***IQ may be 10-15 points lower than average Testing Options *Triple marker screening **Blood test performed at 15-22 weeks gestation **Screening test, not diagnostic ***In whole population, detects 62% of problems ***False positive rate of 3.6% **Indirect measurement of AFP, hCG, and uE3 production **Detects some chromosomal abnormalities associate with maternal age ***Down Syndrome (70% in women older than 35) ***Trisomy 18 (60%) ***Open neural tube defects (80-90%) ***Does not detect all chromosomal abnormalities associated with maternal age **Amniocentesis may be offered to follow-up on results *Ultrasound **Capable of detecting many major birth defects ***May identify ultrasound anomaly that could indicate a chromosomal abnormality ***Cannot diagnose chromosome abnormality based on ultrasound findings **Amniocentesis or CVS may be offered to follow-up on results *Chorionic Villus Sampling (CVS) **Sample of placental tissue (chorionic villi) obtained ***Tissue is from same embryonic origin as fetus ***Should have same genetic composition as fetus **Usually performed at 10-12 weeks gestation **Technique ***Transcervical ****Begin with ultrasound exam to confirm fetal heart activity, appropriate growth, and location of placenta, uterus, and cervix ****Patient placed in lithotomy position ****Vagina and cervix cleaned with betadeine ****Speculum is inserted and some physicians apply a tenaculum to the lip of the cervix to help manipulate the uterus ****Catheter with a stylet inserted is guided into the placenta using US ****Stylet removed and syringe inserted ****Suction is applied to aspirate villi ****May be slightly uncomfortable ***Transabdominal ****Begin with ultrasound exam ****Abdomen cleaned with betadeine and xylocaine injection given to numb skin ****Spinal needle with stylet guided through abdominal and uterine walls into placenta using ultrasound guidance ****Stylet removed and syringe attached ****Suction applied by syringe plunger and needlemoved back and forth ****Can be performed at any time during pregnancy ****May be moderately uncomfortable ***Transcervical vs. transabdominal ****Bleeding more common following transcervical (10%) ****Cramping more common following transabdominal ****No significant difference in risk for fetal loss ****Some reports indicate transcervical may have higher risk for infection ***Recommendations for medical care ****Rh negative women should be given Rhogam ****No exercise or strenuous activity for 24 hours ****No sexual intercourse, douching, tub baths, or use of tampons for 72 hours ****Notify OB if any of the following signs *****Fever above 1000F *****Heavy bleeding or cramping *****Amniotic fluid leakage ****Follow up ultrasound in a few days ****MSAFP at 16-18 weeks ****Ultrasound at 20 weeks to check fetal anatomy **Risks/Benefits of CVS ***98-99% accuracy for fetal chromosome analysis ****Allow identification of affected fetus early in pregnancy ****Maternal cell contamination risk if 46,XX result ****1-2% chance for mosaicism *****Presence of two or more cell lines that differ in chromosome composition *****Difficult to interpret because may arise in vitro in lab, may be confined to placenta and not affect fetus, or may represent true fetal mosaicism ***Can perform molecular DNA analysis or biochemical analysis if at risk fetus ***Can't detect open neural tube defects ***Can't detect all birth defects or mental retardation ***Risk of miscarriage due to procedure is 1% (in addition to 2-3% background risk) ***Some past studies have cited increased risk for transverse limb anomalies ****When performed before 10 weeks ****More recent studies do not indicate any increased risk when performed at 10-12 weeks ***Some women with elevated MSAFP or unclear CVS results may be offered amniocentesis ***Not recommended for women with following conditions ****Active vaginal bleeding ****Maternal bleeding disorder ****Cervical polyps, active genital herpes or other infection (transcervical) ****Interceding bowel or placenta far from maternal abdominal surface (transabdominal) Amniocentesis *Performed after 15 weeks *Risks/Benefits **99.7% accuracy for fetal chromosome analysis **Detects 96% of open neural tube defects by testing AFAFP **Cannot detect all birth defects or mental retardation **Risk of miscarriage due to procedure is 0.5% **Incidence of mosaicism is 0.1-0.3% Notes The information for this outline was last updated in 2001. Material obtained under GFDL Licence from http://en.wikibooks.org/wiki/Handbook_of_Genetic_Counseling